Vaping – Effectiveness as a cessation tool: evidence briefing

Annex: Analysis of the existing evidence

Evidence on vaping as a potentially successful strategy to quit smoking is still limited and research gaps remain. However, the number of primary studies exploring the effectiveness of vaping products as a cessation tool has been growing over the past few years. The systematic reviews and meta-analyses examined in this briefing are presented below in a time sequence from the most recent to the oldest to reflect this:

• An Australian umbrella and systematic review on electronic cigarettes and health outcomes, published in 2023, concluded that e-cigarettes may be beneficial for smokers who use them to completely and promptly quit smoking. In particular, the review highlighted that:
  • There is limited evidence that the use of freebase nicotine e-cigarettes^[2] with clinical support is more efficacious for assisting smoking cessation than NRT, or than no intervention or usual care.
  • There is insufficient evidence on the efficacy of nicotine e-cigarettes for smoking cessation, compared with non-nicotine e-cigarettes.
  • There is insufficient evidence on the efficacy of non-nicotine e-cigarettes for smoking cessation, compared with counselling or NRT.
  • There is insufficient evidence on the efficacy of non-clinical use of freebase nicotine e-cigarettes for assisting smoking cessation.
  • There is no available evidence on the efficacy of nicotine salt products^[3] for assisting smoking cessation.
  • There is limited evidence that the use of nicotine e-cigarettes for assisting smoking cessation results in greater exposure to nicotine (smoking, exclusive e-cigarette use or dual smoking/e-cigarette use) than NRT.

The authors stressed that the risks associated with e-cigarettes, uncertainty about their effects on major clinical outcomes and continued smoking by most users (dual use), render their overall safety and efficacy as a smoking cessation aid unclear.

• The Cochrane living review on electronic cigarettes for smoking cessation (lastly updated in 2022) examined the effectiveness, tolerability and safety of nicotine e-cigarettes to help people who smoke tobacco achieve long-term smoking abstinence^[4]. The review concluded that:
  • There is high ‐ certainty evidence that nicotine e-cigarettes are more efficacious than NRT for smoking cessation (the authors are confident that the true effect lies close to the estimate of the effect).
  • There is moderate ‐ certainty evidence that nicotine e-cigarettes are more efficacious than non-nicotine e-cigarettes (the authors think the true effect is likely to be close to the estimate of effect).
  • There is very low-certainty evidence that nicotine e-cigarettes are more efficacious than usual care/no treatment (the authors have little confidence in the effect estimate).

The main limitations of the evidence pertained to imprecision due to the small number of randomised controlled trials (RCTs), often with low event rates.

The review highlighted the need for more RCTs following participants at six months or longer to reduce the risk of bias and data imprecision. It also stressed how more evidence is needed around the effect of newer types of e-cigarettes which have better nicotine delivery, different flavours and varying nicotine strengths compared to older devices.

• The Public Health England Vaping in England evidence review, published in 2021, concluded that there is stronger evidence compared to their 2018 review that nicotine vaping products are effective for smoking cessation and reduction. The review summarised key findings from:
  • Nationally representative surveys, showing that vaping products were the most popular smoking cessation aid compared to NRT and varenicline, despite all three being positively associated with successfully quitting smoking.
  • English stop smoking services data, showing that: the highest quit rates were seen when the quit attempt involved people using a licensed medicine and a vaping product one after another; quit rates were similar for people using a vaping product and licensed medication at the same time, a vaping product alone and varenicline alone; and quit rates involving a vaping product were higher than any other method in every region in England.
  • Systematic reviews and meta-analyses, three of which were deemed of moderate to high quality and consistently found that vaping products containing nicotine were significantly more effective in helping people quit smoking compared to NRT. Findings of meta-analyses of RCTs confirmed this when studies with a high risk of bias were excluded.

Limitations in the reviewed evidence pertained to: high risk of bias; the use of outdated vaping products (e.g. with low nicotine strength, with no nicotine salts and mostly tobacco-flavoured) in many of the RCTs; and the fact that RCTs don’t necessarily reflect real world circumstances due to strict inclusion/exclusion criteria and adherence to particular intervention measures (e.g. type, dose, duration, frequency).

The review highlighted the need for further research to: assess whether smokers who use stop smoking services and vaping products differ from smokers who use the services and other cessation aids; explore the barriers and enablers to using vaping products as part of a supported quit attempt in stop smoking services; and gather data on newer types of vaping products with better nicotine delivery.

• The US Preventive Services Task Force systematic review, published in 2021, addressed the effectiveness and safety of electronic cigarettes, pharmacotherapy and behavioural interventions for tobacco cessation in adults. The review concluded that:
  • Data on the effectiveness and safety of electronic cigarettes for smoking cessation among adults are limited.

The review highlighted a need for further research that: compares an e-cigarette intervention with no intervention and with the most effective known combination of pharmacotherapy and behavioural support; tests the more recent generations of products; explores use patterns; and investigates the risk of relapse attributable to e-cigarettes.

• The Scientific Committee on Health, Environmental and Emerging Risks (SCHEER) review for the European Commission, published in 2021, synthesised systematic reviews/meta-analyses alongside newly published RCTs, on the use of e-cigarettes for cessation of traditional tobacco smoking. The review concluded that:
  • There is weak evidence to support the effectiveness of electronic cigarettes in helping smokers to quit.
  • The evidence on smoking reduction is weak to moderate.

SCHEER highlighted a lack of robust longitudinal data and noted that existent evidence mostly referred to quitting at six months and did not account for relapse or dual use after the initial six-month period.

The Committee stressed the need for further research to assess the impact of newer vaping products on population based smoking cessation, by means of large population-based cohort data, with sufficient follow-up time to assess potential relapse.

Due to the above limitations, SCHEER recommended that e-cigarettes should only be considered to support smoking cessation for a limited period and under supervision.

• An Irish systematic review and meta-analysis, conducted by the Health Research Board and published in 2020, investigated the safety and efficacy of e-cigarettes in quitting attempts compared to any treatment or combination of treatments usually given for smoking cessation. The authors concluded that:
  • There is no evidence of a difference in effect on incidences of smoking cessation at 24 or 26 weeks between the ENDS (electronic nicotine delivery systems) and the NRT groups.
  • There is a low-level of certainty in these results due to high risk of bias, low successful event rates and high rates lost to follow-up in all studies.

Further limitations identified by the authors were: limited number of longer-term studies beyond 26 weeks; small sample sizes; mixed results due to the comparison of e-cigarettes to different controls in different studies and to non-standardised interventions (i.e. adoption of a variety of first- and second-generation e-cigarettes with varying nicotine doses).

• The Smoking Cessation report of the US Surgeon General, published in 2020, reviewed a number of interventions and treatments for nicotine dependence and concluded that:
  • The evidence is inadequate to infer that e-cigarettes increase smoking cessation.
  • The evidence is suggestive but not sufficient to infer that the use of e-cigarettes containing nicotine is associated with increased smoking cessation compared with the use of e-cigarettes not containing nicotine.
  • The evidence is suggestive but not sufficient to infer that more frequent use of e-cigarettes is associated with increased smoking cessation compared with less frequent use of e-cigarettes.

Reported limitations of the evidence related to: small numbers of trials; low event rates; wide confidence intervals; the diverse and rapidly evolving e-cigarette products; the contexts in which they were used (e.g. if they were used together with behavioural support); lack of comparison to standard evidence-based therapy; lack of control for confounding based on motivation to quit smoking.

The authors hence suggested that well-controlled clinical trials and rigorous, large-scale observational studies with long-term follow-ups are needed to better understand the impact of different types of e-cigarettes under various conditions, including real-world use of e-cigarettes in different regulatory contexts.

• The Public Health Consequences of E-cigarettes report, published by the National Academies of Sciences, Engineering and Medicine (NASEM) in 2018, addressed some research questions about the efficacy of e-cigarettes for smoking cessation. The report concluded that:
  • There is limited evidence that e-cigarettes may be effective aids to promote smoking cessation.
  • There is moderate evidence from RCTs that e-cigarettes with nicotine are more effective than e-cigarettes without nicotine for smoke cessation.
  • There is insufficient evidence from RCTs about the effectiveness of e-cigarettes as cessation aids compared with no treatment or Food and Drug Administration-approved smoking cessation treatments.
  • While evidence from observational trials is mixed, there is moderate evidence from observational studies that more frequent use of e-cigarettes is associated with an increased likelihood of cessation.

Limitations of the evidence pertained to: limited number of studies; limited range of treatment comparisons in RCTs; different study designs which complicated comparison; small sample sizes; risk of bias; failure to measure motivation to quit; and failure in some observational studies to account for covariates which may affect the effectiveness of e-cigarettes for smoking cessation (e.g. e-cigarette product characteristics, pattern of current use and user characteristics).